Brassica oleracea is a species within the genus Brassica in the family of plants known as Cruciferae. Plants of this family are familiarly referred to as Crucifers because of the four-petalled flowers which resemble a cross or crucifix. The Crucifer family is so large that it is broken into sub-groups, referred to as genera. One of the genera of the Crucifer family is the Brassica genus.
Brassica oleracea is a species with a wide range of diverse morphotypes, including cabbage, cauliflower, broccoli, brussel sprouts, kohlrabi, collards, and various kales, commonly known as the cole crops. All of these forms, with the exception of some broccolis, a few cauliflower types, and Chinese kale require a period of cool temperature, i.e., 35.degree.-40.degree. F. for approximately 2-12 weeks, in order to induce the plant from the vegetative to the flowering stage. Under normal seed production of the cole crops, seeds are sown in July or August in regions with a cool, mild winter, such as the Pacific coast of North America, Northern Europe, or Japan. The crop grows into the fall and winter where it undergoes vernalization. As used here, the term "vernalization" means the inducement of flowering by subjecting a growing crop to a low temperature, i.e., about 5.degree. C. The crop flowers in the late spring. Seeds are normally ripe and harvested in August. The entire seed-to-seed life cycle, hereinafter referred to as "life cycle", of the crop takes a little more than one year.
It is well known that the above-listed vegetables are excellent nutrition sources, forming an essential part of the diets of many nations. Additionally, it has recently been discovered that varieties of several Brassica species make excellent resource tools, as the plant may be used as a repository for many genetic mutations of scientific, educational and potential economic interests. Reference is made to Williams, Paul H. and Curtis B. Hill, "Rapid-Cycling Populations of Brassica", Science, Vol. 232, pp. 1385-1389 (Jun. 13, 1986).
The cultivated Brassicas include six interrelated species, three of which (B. nigra, B. campestris, and B. oleracea) and the other three of which are diploids (B. juncea, B. napus, and B. carinata) are amphidiploid derivatives of the diploid species. Stocks of all these species, and the related species of radish, Raphanus sativus, are established, maintained and made available by the Crucifer Genetics Cooperative, Dept. of Plant Pathology, 1630 Linden Drive, Madison, Wis. 53706. Under conventional taxonomy, the three diploid species are assigned genomic descriptors as are their amphidiploid derivatives, with the cytoplasmic genome written in upper case corresponding to the lower case nuclear genome of the species contributing the cytoplasm, i.e. B. campestris (n=10) is Aaa, B. nigra (n=8) is Bbb, B. oleracea (n=9) is Ccc, B. juncea (n=18) is ABaabb, B. carinata (n=17) is BCbbcc, B. napus (n=19) is ACaacc, and R. sativus (n=9) is Rrr. The cytogenetic interrelationships of the six Brassica species have been documented for many years. Morinaga, "Interspecific Hybridization in Brassica VI. The Cytology of F.sub.1 hybrids of B. juncea and B. nigra," Cytology, 6, pp. 62-67 (1934). Since that time numerous studies have demonstrated the feasibility of the interspecific transfer of genes among the various Brassica species. Yarnell, "Cytogenetics of the Vegetable Crop. II. Crucifers." Bot. Rev., 22, pp. 81-166 (1956), McNaughton et al., " Interspecific and Intergeneric Hybridization of the Brassicae with Special Emphasis on the Improvement of Forage Crop," Scottish Plant Br. Sta. 57th Am. Rept. Invergowrie, pp. 75-100 (1978). Thus it is possible, under current technology and using conventional plant breeding techniques, to move genetic traits both within a species and between species in the Brassica genus.
The three diploid species of Brassica, including B. oleracea, are insect pollinated and strongly out-breeding with self incompatibility controlled by a multiple allelic series of genes. The selfing of incompatible plants can, however, be accomplished by bud pollination or by the placement of "self" pollen on the immature stigmas of the plant one to two days prior to anthesis.
Detailed information about Crucifer stocks, husbandry and cultivation, and genetics as well as specific techniques, such as manual pollination, can be found in the Resource Book of the Crucifer Genetics Cooperative and available from it. One of the stocks available from the Crucifer Genetics Cooperative, and available from it, is a population of Brassica oleracea plants referred to as CrGC-3. This is a fast-cycling population of plants, with a mean flower time of 30 days and averaging 23 cm in height. The plants in this population are fully fertile and are now used by plant breeders and researchers in many applications of basic and applied science.